Semiconductor integrated circuit device

ABSTRACT

The invention provides a semiconductor integrated circuit device provided with an SRAM that satisfies the requirements for both the SNM and the write margin with a low supply voltage. The semiconductor integrated circuit device include: multiple static memory cells provided in correspondence with multiple word lines and multiple complimentary bit lines; multiple memory cell power supply lines that each supply an operational voltage to each of the multiple memory cells connected to the multiple complimentary bit lines each; multiple power supply circuits comprised of resistive units that each supply a power supply voltage to the memory cell power supply lines each; and a pre-charge circuit that supplies a pre-charge voltage corresponding to the power supply voltage to the complimentary bit lines, wherein the memory cell power supply lines are made to have coupling capacitances to thereby transmit a write signal on corresponding complimentary bit lines.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Continuation of U.S. application Ser. No.12/662,029 filed on Mar. 29, 2010, which is a Continuation of U.S.application Ser. No. 12/314,190 filed on Dec. 5, 2008, which is aContinuation of U.S. application Ser. No. 11/504,079 filed on Aug. 15,2006, which is a Continuation application of U.S. application Ser. No.11/127,286 filed May 12, 2005. Priority is claimed based on U.S.application Ser. No. 12/662,029 filed on Mar. 29, 2010, which claims thepriority of U.S. application Ser. No. 12/314,190 filed on Dec. 5, 2008,which claims the priority of U.S. application Ser. No. 11/504,079 filedon Aug. 15, 2006, which claims the priority of U.S. application Ser. No.11/127,286 filed May 12, 2005, which claims the priority of JapanesePatent Application No. 2004-267645 filed Sep. 15, 2004, all of which isincorporated by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a semiconductor integrated circuitdevice, specifically to a technique effective in use for a semiconductorintegrated circuit device provided with a static random access memory.

As one of the parameters for evaluating the memory cells of a staticrandom access memory (hereunder, simply referred to as SRAM), the staticnoise margin (hereunder, simply referred to as SNM) is generally used.The SNM indicates the stability of data stored in the memory cells. Asthe value of the SNM becomes increased, the data retaining operation ofthe memory cells becomes more stabilized; on the contrary however, thewriting of inverse data to the retained data stored in the memory cellsbecomes difficult. The Japanese Unexamined Patent Publication No.2002-042476 is disclosed as a technique for solving such a problem. Theinventors of this application examined the circuit construction of theSRAM on the basis of the above publication. FIG. 17 illustrates theblock diagram of the SRAM. The technique of this publication uses avoltage supply circuit as shown in FIG. 18 for reading data, brings asignal WEi into Low level to activate a P-channel MOSFET, and suppliesthe memory cells with the same level voltage as an external supplyvoltage Vcc, thus intending to secure a stable driving. In the writeoperation, the technique brings the signal WEi into High level todeactivate the P-channel MOSFET and activate an N-channel MOSFETinstead, and lowers the internal supply voltage supplied to the memorycells to Vcc−Vth. Thereby, this technique lowers the SNM of the memorycells selected by the word lines and enhances the write margin.

Patent Document 1: Japanese Unexamined Patent Publication No.2002-042476

SUMMARY OF THE INVENTION

The technique of the Patent Document 1 involves lowering the internalsupply voltage supplied to the memory cells of which the word linesselected by the row decoder are activated, which are not selected by thecolumn decoder, and it also involves the danger of disappearing databecause of the influences of noises in the read-out state of the loweredSNM. In order to avoid such danger, the technique of the patent document1 provides an external supply voltage control circuit as shown in FIG.19, which sets a lower limit voltage, and discriminates the lower limitvoltage to thereby restrain the SNM of the non-selected memory cellsfrom being lowered. However, to generate such a lower limit voltage, thetechnique needs to provide an intermediate supply voltage generatorinside the memory. This provision of the intermediate supply voltagegenerator increases the current consumption of the memory circuit, andthe lower limit voltage restrains the lowering of the SNM, thus leadingto incapability of enhancing the write margin. Especially in the LSI(Large Scale Integrated Circuit), the trend for low power consumptionand the trend for micro-structuring the MOSFETs inside the LSI willlower the supply voltage, and the difference between the lower limitvoltage and the supply voltage becomes very small. Under thesecircumstances, the technique of the patent document 1 precedes the SNMas the memory circuit, which will face an impossibility of enhancing thewrite margin.

Therefore, it is an object of the present invention to provide asemiconductor integrated circuit device provided with an SRAM thatsatisfies the requirements for both the SNM and the write margin with alow supply voltage. The foregoing and other objects and novel featuresof this invention will become apparent from the descriptions andappended drawings of this specification.

According to an aspect of the invention, the semiconductor integratedcircuit device include: multiple static memory cells provided incorrespondence with multiple word lines and multiple complimentary bitlines, multiple memory cell power supply lines that each supply anoperational voltage to each of the multiple memory cells connected tothe multiple complimentary bit lines each, multiple power supplycircuits comprised of resistive units that each supply a power supplyvoltage to the memory cell power supply lines each, and a pre-chargecircuit that supplies a pre-charge voltage corresponding to the powersupply voltage to the complimentary bit lines, wherein the memory cellpower supply lines are made to have coupling capacitances to therebytransmit a write signal on corresponding complimentary bit lines.

According to another aspect of the invention, the semiconductorintegrated circuit device includes: multiple static memory cellsprovided in correspondence with multiple word lines and multiplecomplimentary bit lines, multiple memory cell power supply lines thateach supply an operational voltage to each of the multiple memory cellsconnected to the multiple complimentary bit lines each, and multiplepower supply circuits each made of switch MOSFETs in correspondence withthe memory cell power supply lines, which are made OFF during the writeoperation.

Provided with the above construction, the invention achieves enhancingthe write margin to the memory cells corresponding to the selectedcomplimentary bit lines, and it also achieves securing the SNM to thenon-selected memory cells connected to the non-selected complimentarybit lines.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating one embodiment of an SRAMrelating to this invention;

FIG. 2 is a circuit diagram illustrating one embodiment of a powersupply circuit in FIG. 1;

FIG. 3 is a circuit diagram of a memory cell in one embodiment relatingto this invention;

FIG. 4 is a layout chart illustrating one embodiment of a memory cellrelating to this invention;

FIG. 5 is a waveform chart illustrating an example of the operation ofthe SRAM relating to this invention;

FIG. 6 is a block diagram illustrating another embodiment of the SRAMrelating to this invention;

FIG. 7 is a circuit diagram illustrating one embodiment of a powersupply circuit used for the SRAM in FIG. 6;

FIG. 8 is a circuit diagram illustrating another embodiment of the powersupply circuit used for the SRAM in FIG. 6;

FIG. 9 is a circuit diagram illustrating another embodiment of the powersupply circuit used for the SRAM in FIG. 6;

FIG. 10 is a circuit diagram illustrating another embodiment of thepower supply circuit used for the SRAM in FIG. 6;

FIG. 11 is a circuit diagram illustrating another embodiment of thepower supply circuit used for the SRAM in FIG. 6;

FIG. 12 is a circuit diagram illustrating another embodiment of thepower supply circuit used for the SRAM in FIG. 6;

FIG. 13 is a circuit diagram illustrating another embodiment of thepower supply circuit used for the SRAM in FIG. 6;

FIG. 14 is a layout chart illustrating another embodiment of a memorycell relating to this invention;

FIG. 15 is a circuit diagram illustrating one embodiment of a worddriver used for the SRAM in FIG. 1 or FIG. 6;

FIG. 16 is a whole circuit diagram illustrating the one embodiment ofthe SRAM relating to this invention;

FIG. 17 is a block diagram of an SRAM that the inventors of thisapplication examined in advance on the basis of the patent document 1;

FIG. 18 is a circuit diagram of the voltage supply circuit illustratedin the patent document 1; and

FIG. 19 is another circuit diagram of the voltage supply circuitillustrated in the patent document 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates a circuit configuration of the SRAM as one embodimentrelating to this invention. The drawing typically illustrates fourmemory cells, and two word lines WL0 and WLn and complimentary bit lines/BL0, BL0 and /BLm, BLm, which corresponds to the four memory cells. Thememory cell, which is not illustrated here, includes two CMOS inverterscomposed of P-channel MOSFETs and N-channel MOSFETs, of which inputs andoutputs are cross-connected to form a latch circuit as a memory unit andmutually connected input/output points are used as the memory nodes, andN-channel MOSFETs for address selection, which are provided between thecorresponding bit lines /BL and BL. The gates of the MOSFETs for addressselection are connected to the corresponding word lines.

One of the word lines WL0 through WLn is selected by a row decoder. Therow decoder includes a word driver, which will be described later. Therow decoder is supplied with the row-system address signals of theaddress signal. One pair of plural complimentary bit lines /BL0, BL0through /BLm, BLm is connected to a write driver or a sense amplifierthrough a column selection switch. The column selection switch,receiving selection signals YS0 through YSm generated by a columndecoder, selects one pair of the plural complimentary bit lines /BL0,BL0 through /BLm, BLm, and makes the one pair connect to the outputterminals of the write driver and to the input terminals of the senseamplifier.

A control circuit is supplied with a read/write control signal R/W. Thecontrol circuit generates a write signal WE or a sense amplifier controlsignal SAC as a read-out signal, in correspondence with the read/writesignal R/W. The write signal WE is supplied to the write driver, and isused for activating the write driver. Thus, one of the word lines isselected by the row decoder, and one pair of the complimentary bit linesis selected by the column decoder through the column selection switch;and after the write driver is activated, the data input signal iswritten into the memory cell coupled with the selected word line and theselected complimentary bit lines. The sense amplifier control signal SACis used for activating the sense amplifier. In the same manner as theabove, one of the word lines is selected by the row decoder, and onepair of the complimentary bit lines is selected by the column decoderthrough the column selection switch; and after the sense amplifier isactivated, a read-out signal from the memory cell coupled with theselected word line and the selected complimentary bit lines istransmitted to the sense amplifier. The sense amplifier amplifies theread-out signal and outputs the amplified read-out signal as a dataoutput.

This embodiment further includes memory cell power supply lines VCC0through VCCm in correspondence with the complimentary bit lines /BL0,BL0 through /BLm, BLm, in order to enhance the write margin of thememory cell corresponding to the selected complimentary bit lines aswell as secure the SNM of the non-selected memory cells connected to thenon-selected complimentary bit lines. The typically illustrated memorycell power supply line VCC0 is the power supply line to the memory cellconnected to the corresponding complimentary bit lines /BL0, BL0. In thesame manner, the typically illustrated memory cell power supply lineVCCm is the power supply line to the memory cell connected to thecorresponding complimentary bit lines /BLm, BLm. Power supply circuits 0through m are provided between the power supply VCC and the memory cellpower supply lines VCC0 through VCCm.

FIG. 2 illustrates a circuit configuration as one embodiment of thepower supply circuit in FIG. 1. This embodiment uses a P-channel MOSFETQP as the power supply circuit. The gate of the MOSFET QP is constantlygiven the ground potential of the circuit, whereby it works as aresistive element, and the power supply voltage VCC is transmitted to aninternal power supply by column, namely, to the memory cell power supplyline. Here, in the write operation to a memory cell, the potential ofone of the complimentary bit lines /BL and BL varies from a pre-chargelevel such as the power supply voltage VCC to a low level such as theground potential of the circuit; then the potential of the memory cellsupply line temporally drops due to the capacitance coupling with thebit line that has had such a potential variation. The ON-resistance ofthe MOSFET QP is set to have such a comparably large resistance as thetemporary potential drop of the memory cell supply line is allowed.Thus, the operational voltage to the memory cell is lowered in the writeoperation, whereby the SNM is lowered to enhance the write margin. Onthe other hand, both the potentials of the non-selected bit lines /BLand BL are maintained to a high level such as the power supply voltageVCC; accordingly, the corresponding memory cell supply lines are alsomaintained to the power supply voltage VCC. Therefore, in the memorycells of which word lines are put in the selected state, the powersupply voltage is maintained high, so that the SNM can be maintainedhigh.

FIG. 3 illustrates a circuit configuration of the memory cell as oneembodiment relating to this invention. The memory cell includes two CMOSinverters composed of a P-channel MOSFET Q1 and an N-channel MOSFET Q2,and a P-channel MOSFET Q3 and an N-channel MOSFET Q4, wherein inputs andoutputs thereof are cross-connected to form a latch circuit, and anaddress selection switch composed of N-channel MOSFET Q5 and Q6 that areprovided between a pair of input/output nodes N1, N2 of the latchcircuit and the corresponding bit lines /BL, BL. The gates of the MOSFETQ5, Q6 for address selection are connected to the corresponding wordline WL.

In the memory cell in this embodiment, the operational voltage VCC′ tothe memory cell corresponding to the complimentary bit lines /BL and BLis supplied from the memory cell supply line provided between the samecomplimentary bit lines /BL and BL, which is extended in parallel to thebit lines. Concretely, the memory cell supply line is connected to thesources of the P-channel MOSFETs Q1 and Q3 constituting the CMOSinverter. The memory cell supply line as such possesses a parasiticcapacitance C1 between itself and the one complimentary bit line /BL,and possesses a parasitic capacitance C2 between itself and the othercomplimentary bit line BL.

FIG. 4 illustrates a layout of the memory cell as one embodimentrelating to this invention. FIG. 4 (A) illustrates the layout patternsof the sources, drains, and gates of the MOSFETs, and the contactwirings and contact holes; FIG. 4 (B) illustrates the layout patterns ofthe memory cell supply line that supplies the operational voltage VCC′to the bit lines /BL, BL and the memory cell, and the contact wiringsand contact holes; and FIG. 4 (C) illustrates the layout patterns of theground line that supplies the ground potential VSS to the word line WLand the memory cell. The contact holes are illustrated by a square markCNT with a mark x applied.

In FIG. 4 (A), the P-channel MOSFETs Q1 and Q3 are formed in N-WELLsprovided in the center with slash lines applied. On the other hand, theN-channel MOSFETs Q2, Q4 and Q5, Q6 are formed in the P-substrate orP-WELLs except the above N-WELLs. With regard to the MOSFETs Q1, Q2, Q3,Q4 that constitute the CMOS inverter, the gate electrodes thereof areformed integrally. The contact wirings and contact holes each have theindications of connection destination such as WL, /BL, VCC′, BL, WL, andVSS. The MOSFETs Q1, Q2, and Q5 and the MOSFETs Q3, Q4, and Q6 areplaced symmetrically as the former coincides with the latter by therotation of 180° at the center of the memory cell. The wiring layer ofthe contact wirings is indicated by the voided pattern surrounding thecontact holes, and is formed on a metal layer M1 being the first layer,which is not especially specified.

In FIG. 4 (B), the bit lines /BL and BL correspond to the sources anddrains of the MOSFETs Q5 and Q6 ; they are disposed to be verticallyextended in the drawing at parts of ¼ and ¾ among boundaries equallydividing a region of the memory cell into four in a horizontal directionin the drawing, and are formed on a metal layer M2 being the secondlayer, which is not especially specified. The memory cell supply line(VCC′) is formed on the metal layer M2 being the second layer in thesame manner as the bit lines /BL, BL, and is disposed so as tovertically extend at a part of a center ( 2/4) among the boundariesapproximately equally dividing the region of the memory cell into four.The memory cell supply line (VCC′) has a projection that extends towardthe adjoining bit line /BL on the upper part thereof, which serves toconnect the memory cell supply line (VCC′) to the source of theP-channel MOSFET Q1; and it also has a projection that extends towardthe adjoining bit line BL on the lower part thereof, which serves toconnect it to the source of the P-channel MOSFET Q3. This wiring layoutwill form the parasitic capacitance C1 between the bit line /BL and thememory cell supply line (VCC′) and the parasitic capacitance C2 betweenthe bit line BL and the memory cell supply line (VCC′).

In FIG. 4 (C), the word line WL extends horizontally on the centerregion of the memory cell, which is formed on a metal layer M3 being thethird layer. The ground line VSS extends vertically in the memory cellarea, which is formed on a metal layer M4 being the fourth layer. Thisground line VSS is used together with the adjoining ground line VSS.Making up the memory cell as this embodiment makes it easy to form thepower supply lines by column. This makes it possible to form thecoupling capacitances C1, C2 between the bit lines /BL, BL and thememory cell supply line (VCC′).

FIG. 5 illustrates a waveform in the operation of the SRAM relating tothis invention. In the read-out operation of the SRAM, the MOSFETs Q5and Q6 for address selection of the memory cell are made ON by theselection operation of the word line WL, and one of the bit lines /BLand BL is lowered in correspondence with one of the memory nodes N1 andN2 that is put into Low level. Here, the bit lines /B1 and BL havecomparably large capacitances because of multiple memory cells connectedthereto, and the MOSFETTs Q5 and Q6 for address selection havecomparably large on-resistances; accordingly, the lowering level of thebit lines /BL and BL in the read-out signal is slight and the loweringslope thereof is gentle. Therefore, the voltage VCC′ of the memory cellsupply line does not substantially vary to maintain the power supplyvoltage VCC, although there exist the parasitic capacitances (couplingcapacitances) C1 and C2 between the bit lines /BL, BL and the memorycell supply line. This will maintain the static noise margin (SNM) inthe read-out operation at a high level. The slight level difference ofthe bit lines /BL and BL in the read-out signal is amplified by thesense amplifier, which is outputted as the data output.

In the write operation of the SRAM, the MOSFETs Q5 and Q6 for addressselection of the memory cell are made ON by the selection operation ofthe word line. One of the bit lines /BL and BL is lowered sharply to theground potential of the circuit in correspondence with the write signalfrom the write driver. Such sharp lowering with full swing in the writesignal is transmitted to the memory cell supply line through theparasitic capacitances (coupling capacitances) C1 and C2, andtemporarily lowers the operational voltage VCC′ to the memory cell.Thus, the operational voltage VCC′ lowers owing to the couplingcapacitances. However, the operational voltage VCC′ recovers graduallytoward the power supply voltage VCC, since it is supplied with the powersupply voltage VCC through the resistive element of the power supplycircuit. In this duration, one of the bit lines /BL and BL is put intoLow level, and the memory node N1 or N2 is pulled down to Low level fromHigh level through the MOSFET Q5 or Q6 that is made ON according to theselected state of the word line, whereby the stored information of thestorage unit in the memory cell is inversed.

For example, when the memory node N1 is pulled down to Low level fromHigh level, the MOSFET Q1 that maintains High level of the memory nodeN1 lowers the memory node N1 also by the lowering of the memory cellsupply voltage VCC′. At the same time, High level of the bit line BL istransmitted to the gate (memory node N2) of the MOSFET Q2 through theMOSFET Q6, which makes the MOSFET Q2 ON. In this manner, the threefactors overlapped sharply pulls down the memory node N1, which makesthe P-channel MOSFET Q3 ON, thus forming a path that brings the memorynode N2 into High level. As the result, the memory node N1 sharplyvaries from High level to Low level and the memory node N2 sharplyvaries from Low level to High level, which enhances the write margin.Thus, this embodiment will enhance the write margin, if the power supplyvoltage VCC lowers owing to the micro-structuring of devices and soforth to lower the drivability of the write driver.

Here, if the word line WL is selected, the write operation will not beperformed. That is, there does not occur such a voltage drop as theabove even by the coupling with the writing bit line, in the memorycells connected to the non-selected complimentary bit lines /BL and BLfor retaining the stored data; therefore, it is possible to maintain thepower supply voltage VCC in the same manner as the read-out operation.In regard to the memory cells wherein the word line is selected and theMOSFETs Q5,Q6 are made ON, the one to retain the stored data canmaintain a large static noise margin (SNM). In this manner, the voltagevariation in the non-selected column during the write operation and thevoltage variation in the selected bit lines during the read-outoperation are comparably gentle with limited amplitude because of theslight amplitude of the bit lines in the memory cell; and the effect ofthe coupling is limited and the lowering of the SNM is limited to attaina stable operation.

FIG. 6 illustrates a circuit configuration of the SRAM as anotherembodiment relating to this invention. In this embodiment, the samewrite signal WE as that in FIG. 1 is combined with the bit lineselection signals YS0 to YSm formed by the column decoder and gatecircuits G0 to Gm and so forth, which is used for forming activationsignals WC0 to WCm to the write drivers that are provided to the bitlines each. Thus, as the write operation is instructed, the write drivercorresponding to the column address is activated, and the data input iswritten into the memory cell connected to the word line selected by theword driver. On the other hand, as the read-out operation is instructed,the read-out column selection switch becomes ON in correspondence withthe column address, and the signals on the selected bit lines /BL and BLare transmitted to the input of the sense amplifier, which are amplifiedbased on the sense amplifier control signal SAC to be outputted as thedata output.

This embodiment provides the write drivers corresponding to thecomplimentary bit lines /BL0 and BL0 to /BLm and BLm. In such aconstruction, the write signal corresponding to the data input can betransmitted directly to the complimentary bit lines /BL and BL withoutintervention of the column selection switch as the above embodiment inFIG. 1, so that one of the bit lines-pair can be pulled down sharplyfrom the pre-charge level to Low level. In this embodiment, theactivation signals WC0 to WCm are used as the control signals for thepower supply circuits 0 to m that are connected to the memory cellsupply lines VCC0 to VCCm corresponding to the bit lines /BL0 and BL0 to/BLm and BLm each. The other construction is the same as the embodimentin FIG. 1.

FIG. 7 illustrates a circuit configuration of the power supply circuitused for the SRAM in FIG. 6 as one embodiment. In this embodiment, thepower supply circuit is provided with the P-channel MOSFET QP1 in thesame manner as the power supply circuit in FIG. 2 and a P-channel MOSFETQP2 with the activation signal WC connected to the gate thereof, whereinthe two P-channel MOSFETs are connected in parallel. The signal WC isput into High level in correspondence with the selected complimentarybit lines /BL and BL. Accordingly, the P-channel MOSFET QP2 of the powersupply circuit is made OFF in correspondence with the selectedcomplementary bit lines /BL0 and BL0 as an example. Thereby, in thewrite operation, the operational supply voltage VCC′ to the selectedmemory cell is lowered owing to the coupling with the bit lines to whichthe write signal is transmitted. On the other hand, in the power supplycircuits corresponding to the other non-selected complimentary bit linesincluding the non-selected complimentary bit lines /BLm and BLm, boththe P-channel MOSFETs QP1 and QP2 are made ON, and the supply voltageVCC′ to the non-selected memory cells are maintained to be virtuallyequal to the power supply voltage VCC.

In this embodiment, if the on-resistance of the P-channel MOSFET QP1 isset sufficiently high, the coupling capacitances C1, C2 will notnecessarily be needed. The P-channel MOSFET QP2 of the power supplycircuit is made OFF in correspondence with the selected complementarybit lines /BL0 and BL0 as an example, and in consequence only a minutecurrent is supplied from the P-channel MOSFET QP1 having a highresistance. Therefore, through the P-channel MOSFET QP1 as such flow theleakage current in the multiple memory cells connected to thecomplementary bit lines /BL0 and BL0 and the current in the memory cellswherein the inverse writing is performed, which corresponds to theoutput signal variation of the CMOS inverter. Therefore, without theabove capacitance coupling, the operational voltage VCC′ to the memorycell lowers. The lowering of this operational voltage VCC′ will increasethe write margin to the memory cell.

In contrast to this, even if the word line is selected, the writeoperation will not be performed. In regard to the memory cells connectedto the non-selected complimentary bit lines, which have to retain thestored data, the memory cell supply lines are connected to the powersupply voltage VCC with low impedance by the ON-state of the MOSFETs QP1and QP2, so that the memory cell supply lines can be maintained to thepower supply voltage VCC more stably. Thereby, the memory cells toretain the stored data among those wherein the word line is selected andthe above MOSFETs Q5, Q6 are made ON can maintain a large static noisemargin (SNM). Therefore, the layout of the memory cell in thisembodiment is not limited to the one in FIG. 4. For example, the bitlines /BL, BL and the memory cell supply lines VCC′ may be made onseparate wiring layers, thereby expanding the freedom of degree indesigning the circuit layout.

FIG. 8 illustrates a circuit configuration of the power supply circuitused for the SRAM in FIG. 6 as another embodiment. In this embodiment,the power supply circuit omits the P-channel MOSFET QP1 in FIG. 7 andincludes only the P-channel MOSFET QP2 having the activation signal WCsupplied to the gate thereof. In this configuration, the P-channelMOSFET QP2 of the power supply circuit is made OFF in correspondencewith the selected complementary bit lines /BL0 and BL0 as an example,and in consequence, the power supply for all the memory cells thatcorrespond to the selected complementary bit lines /BL0 and BL0 is cutoff. Therefore, through the P-channel MOSFET QP1 as such flow theleakage current in the multiple memory cells connected to thecomplementary bit lines /BL0 and BL0 and the current in the memory cellswherein the inverse writing is performed, which corresponds to theoutput signal variation of the CMOS inverter. Therefore, without theabove capacitance coupling, the operational voltage VCC′ to the memorycell lowers significantly.

Therefore, even if there is a possibility that the operational voltageVCC′ temporarily drops lower than the lower limit for the memory cell,High level and Low level from the write driver are written through theMOSFETs Q5 and Q6 into the capacitances at the memory nodes N1 and N2 ofthe selected memory cell having the word line selected. On the otherhand, in the memory cells having the word line non-selected, the MOSFETsQ5 and Q6 are made OFF; therefore, even if the operational voltage VCC′is brought into a lower level than the lower limit, the capacitances atthe memory nodes N1 and N2 retain charges to be stored. Therefore, evenif the P-channel MOSFET QP2 is made OFF for a short duration requiredfor the write operation to the memory cell, the non-selected memorycells retain the stored data by the charges to be stored in the samemanner as the dynamic memory cells. Thereafter, the P-channel MOSFET QP2is made ON to supply the power supply voltage VCC, thereby to recoverthe temporarily decreased charges to be stored.

In this embodiment, in the state that the power supply for all thememory cells corresponding to the selected complementary bit lines /BL0and BL0 as above is temporarily cut off by the OFF-state of the MOSFETQP2, the static memory cells perform the same storage operation as twodynamic memory cells that have mutually different charged states. Evenwhen part of the charges to be stored at the memory node N1 or N2 aretemporarily disappeared, the inverter is activated by the power supplythat is given by the ON-state of the MOSFET QP2 accompanied with thewrite completion, thereby recovering the original state. This embodimentneeds to set the pulse width of the write signal WE in such a mannerthat the internal power supply VCC′ to the selected column in the writeoperation does not reach the level of erasing the data in thenon-selected memory cells. This embodiment, using a simply configuredpower supply circuit, enhances the write margin of the memory cellcorresponding to the selected complimentary bit lines, and also securesthe SNM of the non-selected memory cells connected to the non-selectedbit lines.

FIG. 9 illustrates a circuit configuration of the power supply circuitused for the SRAM in FIG. 6 as another embodiment. This embodimentincludes an N-channel MOSFET QN1 connected in parallel to the P-channelMOSFET QP2 in FIG. 7. The gates of the N-channel MOSFET QN1 and theP-channel MOSFET QP2 are mutually connected, where the activation signalWC is supplied. In this embodiment, as the P-channel MOSFET QP2 of thepower supply circuit is made OFF in correspondence with the selectedcomplementary bit lines /BL0 and BL0 as an example, the N-channel MOSFETQN1 is made ON instead. Therefore, when the leakage current in themultiple memory cells connected to the complementary bit lines /BL0 andBL0 and the current corresponding to the output signal variation of theCMOS inverter and flowing in the memory cells in which the inversewriting is performed flow, the operational voltage VCC′ to the memorycell will not be lowered to VCC−Vth. Here, Vth represents the thresholdvoltage of the N-channel MOSFET QN1. Thus, as compared to the embodimentin FIG. 8, when the pulse width of the write signal WE is set comparablylarge, there will not be such an apprehension that the data in thenon-selected memory cells are erased.

FIG. 10 illustrates a circuit configuration of the power supply circuitused for the SRAM in FIG. 6 as another embodiment. This embodiment takeson the same configuration as that in FIG. 7, wherein the P-channelMOSFET QP1 is replaced by a resistive element R. This resistive elementR can be replaced by a resistive unit except the MOSFET, such as adiffusion resistor, a poly-silicon resistor, or the like. The operationis the same as that in FIG. 7.

FIG. 11 illustrates a circuit configuration of the power supply circuitused for the SRAM in FIG. 6 as another embodiment. This embodiment is amodified example from the embodiment in FIG. 9. The lower limit voltageis transmitted to the internal power supply by column (memory cellsupply line VCC′) by an N-channel MOSFET QN2. In the embodiment in FIG.9, the power supply circuit supplies the voltage VCC−Vth to the selectedcolumn in the write operation, wherein Vth is the threshold voltage ofthe N-channel MOSFET. This embodiment supplies the lower limit voltageto the memory cell by the N-channel MOSFET QN2. Therefore, the lowerlimit voltage is lower than the voltage VCC−Vth. If the lower limitvoltage is intended to be higher than the voltage VCC−Vth, it is onlyneeded to use a P-channel MOSFET, inverse the activation signal WC by aninverter, and supply the inverted activation signal WC to the gate ofthe P-channel MOSFET that supplies the lower limit voltage. This caseneeds to provide a lower limit voltage generator separately.

FIG. 12 illustrates a circuit configuration of the power supply circuitused for the SRAM in FIG. 6 as another embodiment. This embodiment is amodified example from the embodiment in FIG. 11, which uses thethreshold voltage Vth of a P-channel MOSFET QP3 as the lower limitvoltage. This embodiment includes the P-channel MOSFET QP3 between thememory cell supply line VCC′ and the ground potential VSS. Theactivation signal WC is supplied to the gate of this P-channel MOSFETQP3 through an inverter INV1. This power supply circuit brings theactivation signal WC into High level in correspondence with the selectedbit lines /BL, BL. Thereby, the P-channel MOSFET QP2 is made OFF and theP-channel MOSFET QP3 is made ON in turn. The ON-state of the P-channelMOSFET QP3 lowers the memory cell operational voltage VCC′ down to Vth.Thus, the memory cell connected to the selected bit lines /BL, BL is tooperate with the threshold voltage Vth of the P-channel MOSFET QP3served as the operational voltage.

The leakage current in the multiple word-line non-selected memory cellsconnected to the selected complimentary bit lines /BL, BL and the datainversing current in the word-line selected memory cell are consumed, asalready mentioned. However, the power supply circuit in this embodimentdoes not have the current paths corresponding to the above currents; andthe current consumption is substantially the same as the embodiment inFIG. 8. However, this embodiment does not wait for the lowering of thememory cell operational voltage as the embodiment in FIG. 8. The powersupply circuit in this embodiment brings the MOSFET QP3 into ON in thewrite operation, positively lowers the memory cell operational voltageVCC′ to Vth to complete the writing for a short duration in a state ofincreased write margin, and immediately makes the P-channel MOSFET QP2ON. This configuration is immune to the dispersion of elements and soforth, and facilitates the setting of write time.

FIG. 13 illustrates a circuit configuration of the power supply circuitused for the SRAM in FIG. 6 as another embodiment. This embodimentprovides the memory cell ground lines VSS0 to VSSm corresponding to thecomplimentary bit lines /BL0, BL0 to /BLm, BLm each. The memory cellground line VSS′ in FIG. 13 is the ground line to the memory cellconnected to the corresponding bit lines /BL0, BL0. This embodimentprovides a ground supply circuit as shown in FIG. 13 between the memorycell ground line VSS′ by column and the ground line VSS of the circuit.This embodiment does not have the power supply circuit located on theside of the power supply voltage VCC, as seen in FIG. 1 and FIG. 6; andit also enhances the write margin of the memory cell corresponding tothe selected complimentary bit lines and secures the SNM of thenon-selected memory cells connected to the non-selected complimentarybit lines.

In this embodiment, an activation signal WCB is put into Low level incorrespondence with the selected complimentary bit lines /BL, BL.Thereby, an N-channel MOSFET QN3 is made OFF, and a P-channel MOSFET QP4is made ON. Accordingly, the leakage current flowing through themultiple memory cells connected to the selected complimentary bit lines/BL, BL and the current for the writing operation will flow through theP-channel MOSFET QP4, which raises the memory cell ground potential VSS′by Vth. Thus, the memory cell is given such a low voltage as VCC−Vth forthe write operation, and the power supply circuit in this embodiment isequivalent to that in FIG. 9, which also increases the write margin. Onthe other hand, with regard to the memory cell ground line VSS′corresponding to the non-selected complimentary bit lines /BL, BL, theN-channel MOSFET QN3 is ON, and the ground potential VSS is transmittedas it is. Thereby, the operational voltage to the non-selected memorycells connected to the non-selected complimentary bit lines is VCC, andthe SNM can be secured in the same manner as the above.

The ground supply circuit in this embodiment includes the P-channelMOSFET QP4 and N-channel MOSFET QN3 in a parallel configuration. In thesame manner as shown in FIG. 12, the activation signal WCB inverted bythe inverter INV1 is supplied to the gates of the P-channel MOSFET QP4and N-channel MOSFET QN3. The ground supply circuit can be regarded assubstantially the same as the above power supply circuit. Since thememory cell operates when the potential difference between the powersupply voltage VCC and the ground voltage VSS is given as theoperational voltage, to supply the voltage VCC′ obtained by lowering thepower supply voltage VCC as the above embodiment and to supply thevoltage VSS′ obtained by raising the ground voltage VSS of the circuitis the same in terms of the operation of the memory cell.

In order to raise the ground line to the high level by the capacitancecoupling between the bit lines and itself as seen in the embodiment inFIG. 1, it is only needed to pre-charge the bit lines to Low level anddischarge one of the bit lines to High level such as the power supplyvoltage VCC in correspondence with the input data.

FIG. 14 illustrates a layout of the memory cell as another embodimentrelating to this invention. FIG. 14 (A) and FIG. 14 (C) are virtuallythe same as FIG. 4 (A) and FIG. 4 (C), wherein the marks indicating thewiring layers M1 through M4 are omitted. This embodiment exhibits adevice for increasing the capacitances of the parasitic capacitors C1and C2. The parasitic capacitances can be increased also by widening thewiring width of the power supply line VCC′ and by narrowing the gapbetween the bit line /BL and BL. On the other hand however, theparasitic capacitance between the power supply line VCC′ and othercircuit nodes such as the ground potential of the circuit becomesincreased. Since this parasitic capacitance functions toward impedingthe potential variation by the coupling with the bit lines, the abovemethod cannot be evaluated as an effective measure to reinforce thecoupling capacitance. Now, this embodiment makes the patterns meander soas to equally narrow the gap between the bit line /BL and BL withoutwidening the wiring width of the power supply line VCC′. This methodmakes it possible to increase the parasitic capacitances C1 and C2, yetto maintain the parasitic capacitance between the power supply line VCCand the ground potential of the circuit as it is. Therefore, thisembodiment achieves an effective lowering of the voltage VCC′ to thememory cells in correspondence with the potential variations of the bitlines by the write operation.

FIG. 15 illustrates a circuit configuration of a word driver used forthe SRAM in FIG. 1 or FIG. 6 as one embodiment. This circuit diagramtypically illustrates four word drivers corresponding to four word linesWL0 through WL3 as an example. This embodiment uses the NOR gate as theword driver when High level (1) is defined as the positive logic. Takingthe word driver corresponding to the word line WL0 as an example,P-channel MOSFETs PA0 and PB0 are connected in series between the powersupply voltage VCC and an output terminal (WL0), and N-channel MOSFETsNA0 and NB0 are connected in parallel between the ground potential VSSof the circuit and the output terminal (WL0). The gates of the P-channelMOSFET PA0 and N-channel MOSFET NA0 are mutually connected, where aninput signal PDA [0] is supplied; and the gates of the P-channel MOSFETPB0 and N-channel MOSFET NB0 are mutually connected, where an inputsignal PDB [0] is supplied.

The source of the P-channel MOSFET PA0 is supplied with the power supplyvoltage VCC, and the drain of the P-channel MOSFET PB0 is connected tothe output terminal (WL0). This output terminal is connected to the wordline WL0. The sources of the N-channel MOSFETs NA0 and NB0 are suppliedwith the ground potential VSS of the circuit; and the drains of theN-channel MOSFETs NA0 and NB0 are mutually connected to the outputterminal (WL0).

This embodiment uses the P-channel MOSFET PA0 also as the word drivercorresponding to the word line WL1, though not especially specified. Inthe word driver corresponding to the word line WL1, the P-channelMOSFETs PA0 and PB1 are connected in series, and the N-channel MOSFETsNA1 and NB1 are connected in parallel between the ground potential VSSof the circuit and an output terminal (WL1). The gates of the P-channelMOSFET PA0 and an N-channel MOSFET NA1 are mutually connected, where theinput signal PDA [0] is supplied; and the gates of the P-channel MOSFETPB1 and an N-channel MOSFET NB1 are mutually connected, where an inputsignal PDB [1] is supplied.

In regard to the remaining two word lines WL2 and WL3, the correspondingtwo word drivers share a P-channel MOSFET PA2 of which source isconnected to the power supply voltage VCC. That is, in the word drivercorresponding to the word line WL2, in the same manner as the above,P-channel MOSFETs PA2 and PB2 are connected in series between the powersupply voltage VCC and an output terminal (WL2), and N-channel MOSFETsNA2 and NB2 are connected in parallel between the ground potential VSSof the circuit and the output terminal (WL2). The gates of the P-channelMOSFET PA2 and N-channel MOSFET NA2 are mutually connected, where aninput signal PDA [1] is supplied; and the gates of the P-channel MOSFETPB2 and N-channel MOSFET NB2 are mutually connected, where the inputsignal PDB [0] is supplied.

The P-channel MOSFET PA2 is also shared by the word driver correspondingto the word line WL3. That is, in the word driver corresponding to theword line WL3, the P-channel MOSFET PA2 and a P-channel MOSFET PB3 areconnected in series between the power supply voltage VCC and an outputterminal (WL3), and N-channel MOSFETs NA3 and NB3 are connected inparallel between the ground potential VSS of the circuit and the outputterminal (WL3). The gates of the P-channel MOSFET PA2 and N-channelMOSFET NA3 are mutually connected, where the input signal PDA [1] issupplied; and the gates of the P-channel MOSFET PB3 and N-channel MOSFETNB3 are mutually connected, where the input signal PDB [1] is supplied.

The input signals PDA [0] and PDA [1] are in the complimentary(exclusive) relation during the active operation, and when one is set toHigh level, the other becomes Low level. In the same manner, the inputsignals PDB [0] and PDB [1] are in the complimentary (exclusive)relation during the active operation, and when one is set to High level,the other becomes Low level. These input signals PDA and PDB includeclock signal and standby signal components as described later, inaddition to the address signal, through not especially specified.

The input signal PDA is set to the upper bits of the address signal, andthe input signal PDB is set to the lower bits thereof, which is notespecially specified. Accordingly, when the input signal PDA [0] is atLow level and the input signal PDA [1] is at High level, and the inputsignal PDB [0] is at Low level and the input signal PDB [1] is at Highlevel, the P-channel MOSFETs PA0 and PB0 become ON and the N-channelMOSFETs NA0 and NB0 become OFF, in correspondence with Low level of theinput signal PDA [0] and Low level of the input signal PDB [0]. Thereby,the word line WL0 is put into the selected state of High level such asthe power supply voltage VCC. In the word drivers corresponding to theother word lines WL1 through WL3, High level of the input signal PDA [1]makes any one of the two P-channel MOSFETs OFF, and makes any one of thetwo N-channel MOSFETs ON; and the word lines WL1 through WL3 are putinto the non-selected state of Low level such as the ground potentialVSS.

In the standby state, all of the input signals PDA [0], PDA [1] and theinput signals PDB [0], PDB [1] are put into High level. Thereby, all ofthe P-channel MOSFETs are made OFF, and all of the N-channel MOSFETs aremade ON. Now, if there is a leakage current flowing through theP-channel MOSFETs, as mentioned above, the potentials at the nodes ofthe series connected MOSFETs will rise from VSS toward VCC/2, and thesource potentials of the P-channel MOSFETs PA1, PA2 on the side of thepower supply voltage VCC will rise, leading to the so-called sourcebiasing effect wherein the sources are reverse biased to the substrate,thereby making it possible to reduce the leakage current to a greatextent.

When the word line WL0 is in the selected state, both the P-channelMOSFETs PA0 and PB0 or at least any one of PA0 and PB0 of thecorresponding word driver become OFF. The word driver can reduce theleakage current by the source biasing effect attained by thelongitudinal stacking of the P-channel MOSFETs being the feature of theNOR logic gates. Especially in the standby state, wherein all of theinput signals PDA [0], PDA [1] and the input signals PDB [0], PDB [1]become High level, all of the P-channel MOSFETs are made OFF, and thesource biasing effect remarkably reduces the leakage current. Althoughthe P-channel MOSFETs PA0, PA2 are supplied to the two word drivers, asthis embodiment, the two word lines are not selected at the same time,which enhances the leakage reduction effect while maintaining thedrivability. It is possible to increase the number of the shared worddrivers by the power of 2 depending on the decoding logic.

The word driver in this embodiment is characterized in that any specialcontrol signal for reducing the leakage current is not needed. When theinput signal PDA is made to include the clock signal components, namely,when the bit lines are pre-charged, all the word lines are necessarilymade non-selected. In the non-selected state of all the word linesduring the pre-charge, the leakage current can be reduced by the abovesource biasing effect. That is, the leakage current can be reduced notonly in the standby state but also in the accessing state to the memory.

As already mentioned, the power supply voltage to the LSI (Large ScaleIntegrated Circuit) is gradually lowered accompanied with the trend forlow power consumption and the trend for micro-structuring the MOSFETsinside the LSI. By the 0.13 □m process, for example, the LSI beingoperational with the power supply voltage 1.2 V is manufactured. Whenlowering the power supply voltage to an LSI, the general practice lowersthe threshold voltage (Vth) of transistors and increases the currentflowing through the transistors in order not to deteriorate the circuitperformance (operational speed of the circuit). The 0.13 □m process usesthe MOSFETs of which Vth is about 0.4 V, for example. In a transistorwith a low Vth increases the so-called sub-threshold current, namely,the current flowing across the source-drain in the OFF-state of thetransistor. The sub-threshold current continues to flow even when thecircuit configured with this transistor is not operational, which makesa current consumption in the state that an LSI is electrified but is notin operation (standby state). The memory circuit needs to retain thedata even in the standby state, and the power supply cannot bedisconnected even in the standby state. Therefore, the above word driveris able to solve the problem that the sub-threshold current increasesaccompanied with the lowering of Vth of the transistors constituting thecircuit to thereby increase the current consumption in the standbystate.

FIG. 16 illustrates the whole circuit configuration of the SRAM relatingto this invention as one embodiment. The SRAM includes a memory cellarray; an address selection circuit, read-out circuit, and write circuitthat are provided as the peripheral circuits thereof; and a timinggeneration circuit that controls the operations thereof.

The circuit diagram typically illustrates one word line WL, two pairs ofcomplimentary bit lines /BL, BL, and two memory cells placed at theintersections thereof as a memory cell. The memory cell includes twoCMOS inverters composed of P-channel MOSFETs Q1, Q3 and N-channelMOSFETs Q2, Q4, wherein the inputs and outputs thereof arecross-connected to form a latch circuit, and a selection switch composedof N-channel MOSFETs Q5 and Q6 that are provided between a pair ofinput/output nodes of this latch circuit and a pair of the bit lines/BL, BL. The gates of the MOSFET Q5, Q6 are connected to the word lineWL.

In the memory cell array, 128 memory cells are arrayed on one word lineWL, through not especially specified. Accordingly, the memory cell arrayincludes 128 pairs of complimentary bit lines /BL, BL. 256 memory cellsare arrayed on one pair of the bit lines /BL and BL. 256 word lines WLare provided accordingly. The pre-charge & equalizing circuit PC/EQincludes a P-channel MOSFET that supplies a pre-charge voltage to thecomplimentary bit lines /BL and BL and a P-channel MOSFET thatshort-circuits the bit line /BL and BL. This embodiment also includes aP-channel MOSFET having the gate and drain cross-connected between thebit lines /BL, BL and the power supply terminal, as a pull-up MOSFET.Thereby, the potential lowering of the bit line on the High level sidecan be prevented during the read-out.

The 128 pairs of bit lines are connected to 32 pairs of complimentaryread-out data lines /RD, RD by a read-out column switch includingP-channel MOSFETs, through not especially specified. One of the read-outdata lines /RD, RD is connected to either one of four pairs of the bitlines /BL, BL. The read-out data lines /RD, RD are provided with senseamplifiers SA. The sense amplifier SA includes a CMOS latch circuitwherein inputs and outputs of two CMOS inverters composed of P-channelMOSFETs and N-channel MOSFETs are cross-connected, and N-channel MOSFETsprovided between the sources of the N-channel MOSFETs of the CMOS latchcircuit and the ground potential of the circuit. In correspondence withthe 32 pairs of read-out data lines /RD, RD, 32 units of the senseamplifiers SA are provided in total.

Timing signals generated by the timing generation circuit and a timingcontrol signal φsac generated by a gate circuit that receives a senseamplifier selection signal sac are transmitted through an inverterstring that forms control pulses to the gates of the N-channel MOSFETsthat activate the sense amplifiers SA and to the gate circuits thattransmit signals amplified by the sense amplifiers SA. The timingcontrol signal φsac is also used as a selection signal for the read-outcolumn switch. The sense amplifier SA is activated by the selectionsignal and amplifies the signal on the read-out data lines /RD, RD.

The amplified signal by the sense amplifier SA is transmitted to a latchcircuit LT including MOSFETs Q17 through Q22, and an output signal doutis generated by an output circuit OB. The latch circuit LT is formedwith a through-latch circuit being controlled by a signal φolc generatedon the basis of an output latch control signal olc. The output circuitOB includes a gate circuit controlled by a signal φodc generated on thebasis of an output driver control signal odc and an output inverter.

The SRAM in this embodiment is made capable of selecting the read-outoperation that activates all of the 32 sense amplifiers SA to output theread-out signal of 32-bits, the read-out operation that activates 16units of the 32 sense amplifiers SA to output the read-out signal of16-bits, or the read-out operation that activates 8 units of the 32sense amplifiers SA to output the read-out signal of 8-bits, which isnot especially specified. The sense amplifier selection signal sac isused for controlling the sense amplifiers SA in correspondence with thethree types of the read-out operations, and it is also used as thenon-selection signal for the read-out column switch including P-channelMOSFETs, by means of a read switch control signal rswc and a columnselection signal sel.

The 128 pairs of bit lines are connected to 32 pairs of complimentarywrite data lines /WD, WD by write column switches (WCP) includingN-channel MOSFETs. One of the write data lines /WD, WD is connected toany one of four pairs of the bit lines /BL, BL. The write data lines/WD, WD are provided with a write circuit (write amplifier) thatincludes an inverter string (WDP1) that transmits a write signal din tothe write data line WD, an inverter (WDP3) that generates an invertedwrite signal, and an inverter string (WDP2) that transmits the invertedwrite signal to the write data line /WD. This write circuit is alsocomposed of 32 units in correspondence with the 32 pairs of thecomplementary write data lines /WD, WD.

The SRAM in this embodiment is made capable of selecting the writeoperation that validates the write signal of 32-bits generated by the 32write amplifiers, the write operation that validates the write signal of16-bits generated by 16 units of the 32 write amplifiers, or the writeoperation that validates the write signal of 8-bits generated by 8 unitsof the 32 write amplifiers, through not especially specified. A writeswitch control signal wswc is used for the above write operation. Thecolumn selection signal combined with the write switch control signalwswc is transmitted to the write column switches (WCP) includingN-channel MOSFETs.

The amplified signal by the sense amplifier SA is transmitted to theMOSFETs Q17 through Q22 through a gate circuit and to a latch circuitincluding inverters, where the output signal dout is generated throughthe gate circuit and the output inverter. The timing signals generatedby the timing generation circuit and the timing control signal φsacgenerated by the gate circuit that receives the sense amplifierselection signal sac are transmitted through the inverter string thatforms control pulses to the gates of the N-channel MOSFETs that activatethe sense amplifiers SA and to the gate circuits that transmit thesignals amplified by the sense amplifiers SA. The timing control signalφsac is also used as a selection signal for the read-out column switch.

Receiving multiple control signals such as a clock CLK, read/writecontrol signal R/W, etc., the timing generation circuit generatesvarious timing signals required for the operations of the SRAM incorrespondence with various operation modes such as the read-out, write,and standby mode or the like.

One of the 256 word lines WL is selected by a pre-decoder and the worddriver (NOR). The pre-decoder, receiving the timing signals (clock,enable) generated by the timing generation circuit and the addresssignal add, generates a pre-decoded signal and column selection signal.In the standby mode, all the word lines are put into the non-selectedlevel regardless of the address signal add. The column selection signalgenerated by the pre-decoder is used for generating the control signalssac, rswc, wswc, etc., in correspondence with the 32-bits operation,16-bits operation, and 8-bits operation.

The invention made by the inventors of this application being describedin detail based on the preferred embodiments, this invention is notlimited to these embodiments, and various changes and modifications arepossible without a departure from the spirit and scope of the invention.For example, with regard to the number of the word lines and bit linesthat form the memory cell arrays of the SRAM mounted on a semiconductorintegrated circuit device, various configurations can be adopted. TheSRAM of this invention can also be applied to an SRAM for ageneral-purpose memory in addition to the SRAM incorporated into asystem LSI. This invention can widely be applied to the semiconductorintegrated device including the above SRAMs.

What is claimed is:
 1. A semiconductor integrated circuit devicecomprising: a memory cell array including a plurality of memory cellsarranged in a plurality of rows and a plurality of columns, each of thememory cells including first and second storage nodes, a first inverter,an input of which is connected to the first storage node and an outputof which is connected to the second storage node, including a firstp-channel transistor (Q3) and a first n-channel transistor (Q4), asecond inverter, an input of which is connected to the second storagenode and an output of which is connected to the first storage node,including a second p-channel transistor (Q1) and a second n-channeltransistor (Q2), a third n-channel transistor (Q5) connected to thefirst storage node, and a fourth n-channel transistor (Q6) connected tothe second storage node; a plurality of word lines (WL0-WLn) providedcorresponding to the plurality of rows, respectively, each word lineextending in a first direction and being connected to gate electrodes ofthe third and fourth n-channel transistors of the memory cells arrangedin the corresponding row; a plurality of bit line pairs providedcorresponding to the plurality of columns, respectively, each bit linepair having a first bit line (/BL0-/BLm) extending in a second directionand being connected to the third n-channel transistors of the memorycells arranged in the corresponding column and a second bit line(BL0-BLm) extending in the second direction and being connected to thesecond n-channel transistors of the memory cells arranged in thecorresponding column, each bit line pair transmitting data from aselected memory cell for read operation and data to a selected memorycell for write operation; a plurality of memory cell power supply lines(VCC0-VCCm) provided corresponding to the plurality of columns,respectively, so that each memory cell power supply line is arrangedbetween the first and second bit lines of the bit line pair provided forthe corresponding column, each memory cell power supply line connectedto source electrodes of the first and second p-channel transistors inthe memory cells arranged in the corresponding column, a power supplyline (VCC) that supplies a power voltage; a plurality of powertransistors (QP, QP1, QP2, QN1) provided corresponding to the pluralityof columns, each third p-channel transistor being in an on-state to makean conductive pass between the power supply line and the memory cellpower supply line provided for the corresponding column, wherein, ineach of the plurality of memory cells, the first n-channel transistor,the first p-channel transistor and the third n-channel transistor arearranged linearly along the first direction with the first p-channeltransistor located between the first and third n-channel transistorwhile gate electrodes of the first n-channel transistor and the firstp-channel transistor are formed of an integral conductive layer, thesecond n-channel transistor, the second p-channel transistor and thefourth n-channel transistor are arranged linearly along the firstdirection with the second p-channel transistor located between thesecond and fourth transistor while gate electrodes of the secondn-channel transistor and the second p-channel transistor are formed ofan integral conductive layer, the second and third n-channel transistorsare arranged along the second direction and have respective pair of thefirst and fourth n-channel transistors are arranged along the seconddirection.
 2. The semiconductor device according to claim 1, wherein theplurality of power transistors have respective gate electrodes receivingcontrol signals for tuning on and off the respective power transistors.3. The semiconductor device according to claim 2, further comprising acontrol circuit (G0-Gm, COLUMN DECODER) generating the controls signals(WC0-WCm) so that each of the plurality of power transistor (QP, QP1,QP2) is in an off-state when the bit line pair of the correspondingcolumn is selected for the write operation.
 4. The semiconductor deviceaccording to claim 3, wherein each of the plurality of power transistor(QP, QP1, QP2) is in an on-state in the read operation and when the bitline pair of the corresponding column is not selected for the writeoperation.
 5. The semiconductor device according to claim 1, furthercomprising: a column decoder (COLUMN DECODER) decoding an address tooutput selection signals (YS0-YSm) for designating a selected column bythe address, wherein the plurality of power transistor have respectivegate electrode receiving control signals based on the selection signal.6. The semiconductor device according to claim 1, further comprising: aplurality of gate circuits (Go-Gm) generating control signals,respectively, wherein the plurality of power transistor have respectivegate electrode receiving the control signals, respectively.
 7. Thesemiconductor device according to claim 6, further comprising: a columndecoder (COLUMN DECODER) decoding an address to output selection signals(YS0-YSm) for designating a selected column by the address, wherein theplurality of gate circuits have respective first inputs receivingselection signals, respectively, and respective second inputs receivinga common signal (WS) having a first logical value in the read operationand a second logical value in the write operation.
 8. The semiconductordevice according to claim 1, wherein each of the plurality of powertransistors is an p-channel transistor (QP, QP1, QP2) having a sourceelectrode connected to the power supply line and a drain electrodeconnected to the memory cell power supply line provided for thecorresponding column.